Quad flat pack integrated circuit package

ABSTRACT

A quad flat pack (QFP) integrated circuit package that is modified to include a tab that increases the thermal efficiency of the package. The package contains an integrated circuit that is mounted to a die paddle of a lead frame. A plurality of leads extend from a first side of the die paddle. Placing all of the leads on one side of the package minimizes the difference in signal length between the leads. The tab extends from a second side of the die paddle. Both the leads and the tab extend from a plastic housing which encapsulates the integrated circuit. The tab provides a large conductive area which increases the heat transfer rate from the integrated circuit to the ambient, or an external thermal element.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an integrated circuit package.

2. Background Information

Integrated circuits are typically assembled to a package that is mountedto a printed circuit board. There have been developed many types ofintegrated circuit packages including quad flat pack (QFP), ceramic pingrid array (PGA) and ball grid array (BGA) packages.

QFP packages contain a metal lead frame that has a plurality ofindividual leads which extend from a center die paddle. The die paddlesupports the integrated circuit. The integrated circuit has a number ofbond pads that are wire bonded to the individual leads. The integratedcircuit and a portion of the lead frame are encapsulated with aninjection molded plastic housing. QFP packages are relatively simple toassemble and inexpensive to produce. Unfortunately, QFP packages have arelatively high lead to lead spacing so that the density of the packagepins is relatively low. It is generally desirable to have a high pindensity to provide a large number of signal lines in a small amount ofspace. Additionally, the outer plastic housing of a QFP package has alow coefficient of thermal conductivity. QFP packages therefore do notefficiently remove heat generated by the integrated circuits.Consequently, QFP packages typically house relatively low power devices.

PGA packages include a plurality of pins that extend from a housingwhich encloses an integrated circuit. The pins of the package aremounted to an external printed circuit board. PGA package housings aretypically constructed from a ceramic material, or a plastic/printedcircuit board process, which create relatively high pin densities.

PGA packages typically include heat slugs and heat sinks thatefficiently remove heat from the integrated circuit. Consequently, highpowered integrated circuits such as microprocessors are typicallypackaged within PGA packages. Unfortunately, PGA packages are moreexpensive to produce than QFP products.

BGA packages have a plurality of solder balls that are attached to asubstrate. The substrate may be constructed from ceramic or printedcircuit board processes. Like PGA packages, BGA's provide high pindensities and may include a thermal element to remove heat generated bythe integrated circuit. Unfortunately, BGA packages are also relativelyexpensive to produce.

There is always a desire to increase the memory and I/O busses of asystem. The memory bus runs from a package that contains amicroprocessor to a package(s) that contains a memory device(s). Thepackages are typically coupled together by a motherboard. Presentpackages typically provide leads, pins or solder balls in twodimensional arrays. The two dimensional arrays create variations insignal lengths between packages. It is desirable to provide equal signalpaths for each data signal to minimize the slew between signals.Excessive signal slew may create data corruption, particularly for highspeed busses. It would be desirable to provide an integrated circuitpackage which is thermally efficient, inexpensive to produce, andminimizes the difference in signal lengths between signal lines.

SUMMARY OF THE INVENTION

An integrated circuit package that includes an integrated circuit whichis mounted to a die paddle area of a lead frame. The lead frame includesat least two leads extending from a first side of the die paddle areaand a tab that extends from a second side of the die paddle area. Thepackage includes a housing that surrounds the integrated circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top cross-sectional view of an integrated circuit package ofthe present invention;

FIG. 2 is a side view showing a package mounted to a printed circuitboard;

FIG. 3 is a side view showing a package mounted to a printed circuitboard;

FIG. 4 is a side view of an electrical assembly;

FIG. 5 is an end view of an electrical assembly;

FIG. 6 is a top view of a lead frame reel;

FIG. 7 is a top view showing integrated circuits mounted to the leadframes of the reel;

FIG. 8 is a top view showing housings formed about the integratedcircuits;

FIG. 9a is a top cross-sectional view showing an alternate embodiment ofthe package;

FIG. 9b is a top cross-sectional view showing an alternate embodiment ofthe package;

FIG. 10 is a side view of an electrical assembly;

FIG. 11 is a front view of the electrical assembly of FIG. 10.

DETAILED DESCRIPTION OF THE INVENTION

As one embodiment, the present invention is a quad flat pack (QFP)integrated circuit package that is modified to include a tab thatincreases the thermal efficiency of the package. The package contains anintegrated circuit that is mounted to a die paddle of a lead frame. Aplurality of leads extend from a first side of the die paddle. Placingall of the leads on one side of the package minimizes the difference insignal length between the leads. The tab extends from a second side ofthe die paddle. Both the leads and the tab extend from a plastic housingwhich encapsulates the integrated circuit. The tab provides a largeconductive area which increases the heat transfer rate from theintegrated circuit to the ambient, or an external thermal element. Thepresent invention thus provides a relatively inexpensive QFP packagethat can remove heat more efficiently than QFP packages of the priorart.

FIG. 1 shows one embodiment of an integrated circuit package 10 of thepresent invention. The package 10 includes a lead frame 12. The leadframe 12 is typically constructed from a conductive material such ascopper. The lead frame 12 includes a die paddle area 14 that supports anintegrated circuit 16. Although an integrated circuit is shown anddescribed, it is to be understood that other electrical devices may beincorporated into the package 10.

The lead frame 12 has a plurality of leads 18 that extend from one sideof the die paddle 14. The leads 18 are electrically connected to bondpads 20 of the integrated circuit 16 by bond wires 22.

The lead frame 12 further has a tab 24 that extends from the die paddlearea 14. The tab 24 may, or may not be, electrically connected to a bondpad(s) 20 of the integrated circuit 16. In one embodiment the tab 24 mayprovide an electrical ground plane. The tab 24 may have one or moreopenings 26 to allow molten plastic material to more readily flowthrough the lead frame 12.

The integrated circuit 16 and a portion of the lead frame 12 areencapsulated by a housing 28. The housing 28 is typically formed with aninjection molded plastic process. The package 10 is constructed so thatat least a portion of the leads 18 and the tab 24 extend from thehousing 28.

As shown in FIG. 2, the leads 18 are bent into a configuration thatallows the package 10 to be mounted to a printed circuit board 30. Theleads 18 are typically soldered to solder pads 32 of the board 30. Apair of feet 34 may also be bent from the tab 24 and attached to theprinted circuit board 30. The feet 34 can be stamped from the tab 24 orformed by any other process. The feet 34 can be attached to the printedcircuit board 30 by soldering the same to solder pads 32 of the board30. The feet 34 provide structural support so that the package 10 is notcantilevered from the board 30. Alternatively, the entire tab 24 can bebent and attached to the board 30. FIG. 3 shows an embodiment where theleads 18 are bent in a shape that allows the package 10 to be mounted ina position that is perpendicular to the surface of the board 30.

The tab 24 provides a thermal element that has a lower thermalresistance than a conventional QFP package which has individual leadsextending from both sides of the die paddle. A heat sink (not shown) orother additional thermal element can be attached to the tab 24 portionwhich extends from the package 10. Extending the leads 18 from only oneside of the package 10 also minimizes the signal length between theintegrated circuit 16 and another package mounted to the board 30.Creating equal distances minimizes the slew between digital signals thatare provided on the leads 18 and routed through the board 30.

FIGS. 4 and 5 show a plurality of packages 10 that are mounted to theprinted circuit board 30. The packages 10 can be attached to just oneside of the circuit board 30, or both sides of the board. A metal clip36 can be coupled to the tabs 24 of each package 10. The clip 36 mayextend around the edge of the printed circuit board 30 to thermallycouple the packages 10 on each side of the board 30. The clip 36provides a heat spreader that can more evenly distribute the heat loadof the packages. As shown in FIG. 5, the clip 36 may have a heat sink 38to increase the surface area and the thermal efficiency of the overallassembly. Although a clip 36 which extends around the edge of the board30 is shown and described, it is to be understood that the clip 36 maybe attached to only one side of the circuit board 30.

FIG. 6 shows a metal template 40 that contains a plurality of leadframes 12 that are used to construct a number packages 10. Theindividual leads 18 and tabs 24 are typically etched or stamped from asheet of copper material. As shown in FIG. 7, integrated circuits 16 arethen mounted to the die paddle areas 14 and wire bonded to the leads 18,and possibly the tabs 24. The template 40 is then placed within a mold(not shown). Plastic is injected into the mold to encapsulate theintegrated circuits 16 and portions of the lead frames 12 as shown inFIG. 8. The leads 18 and tabs 24 of each lead frame 12 are then cut fromthe template 40 and bent into an appropriate shape for subsequentmounting to a higher level assembly.

FIG. 9 shows an alternate embodiment of a package 50 which has aplurality of leads 52 that extend from opposing sides of a die paddlearea 54 and a pair of tabs 56 that extend from opposing sides of thepaddle 54. The leads 52, and possibly the tabs 56, may be coupled to thebond pads 58 of an integrated circuit 60 by wire bonds 62. Theintegrated circuit 60 and a portion of the leads 52 and tabs 56 areencapsulated by a housing 64.

FIGS. 10 and 11 show an electrical assembly which contains a pluralityof packages 50 mounted to a printed circuit board 66. A metal cover 68can be attached to the circuit board 66 and thermally coupled to thetabs 56 of the packages 50. The metal cover 68 can be bent into aconfiguration which creates contact between the cover 68 and the tabs56.

While certain exemplary embodiments have been described and shown in theaccompanying drawings, it is to be understood that such embodiments aremerely illustrative of and not restrictive on the broad invention, andthat this invention not be limited to the specific constructions andarrangements shown and described, since various other modifications mayoccur to those ordinarily skilled in the art.

What is claimed is:
 1. An integrated circuit package, comprising:a leadframe which has a die paddle area, at least two leads extending from afirst side of said die paddle area and a tab that extends from a secondside of said die paddle area; an integrated circuit that is mounted tosaid die paddle area and coupled to said leads; and, a housing thatsurrounds said integrated circuit.
 2. The package as recited in claim 1,wherein said leads extend from said housing and are bent at a rightangle.
 3. The package as recited in claim 1, wherein said leads extendfrom said housing and are bent into an S-shape.
 4. The package asrecited in claim 1, wherein said lead frame has two sets of leadsextending from opposite sides of said die paddle, and two tabs that eachextend from an opposite side of said die paddle.
 5. The package asrecited in claim 1, wherein said tab has an opening.
 6. The package asrecited in claim 1, wherein said tab has a pair of feet.